The present invention relates to a method and system for device fabrication on a substrate and, more particularly, to a method and system for transferring energy from a radiative energy source to a substrate for rapid thermal processing applications in support of microelectronic and semiconductor device fabrication.
Semiconductor devices can be formed on silicon wafer substrates by the use of certain fabrication processes some of which involve the application of heat (e.g., in the range of 200xc2x0 C. to 1100xc2x0 C.) to the substrate in a controlled environment. Several processing methods for fabricating a device onto a substrate have evolved which include the application of thermal energy to the substrate to drive thermally activated fabrication processes. For instance, chemical-vapor deposition (CVD) processes can deposit various materials on a substrate, including metallic, semiconductor and insulating material layers. Thermal deposition processes and thermal anneal processes can support silicide formation. These chemical and thermal processes can form a microelectronic device such as an insulated gate field-effect transistor (IGFET) on a substrate by manipulating, forming or modifying materials such as silicon dioxide, silicon nitride, tungsten, polysilicon and other known materials. Well-known single-wafer rapid thermal processing (RTP) applications include rapid thermal annealing (RTA), rapid thermal oxidation (RTO), rapid thermal chemical-vapor deposition (RTCVD) processes, and rapid thermal nitridation (RTN).
During the formation of a device such as an IGFET on a substrate by thermal processing techniques such as RTP methods, consistent production of a high-quality semiconductor integrated circuit (IC) with high production yield is enabled when the thermal energy is applied in a uniform and repeatable manner. CVC, Inc. (xe2x80x9cCVCxe2x80x9d) has introduced several significant improvements over conventional thermal processing systems and methods for semiconductor IC fabrication. For instance, CVC has developed a multi-zone radiant-energy illuminator for producing heat in silicon substrates during device fabrication as is disclosed in U.S. patent application Ser. No. 08/678,321 filed on Jul. 11, 1996, and entitled xe2x80x9cMulti-Zone Illuminator for Rapid Thermal Processing,xe2x80x9d which is incorporated herein by reference as if fully set forth. This multi-zone illuminator provides improved wafer-to-wafer process and temperature repeatability as well as within-wafer temperature uniformity by monitoring and controlling optical energy produced by plural lamps arranged in multiple heating zones. The multi-zone illuminator also includes a multi-zone temperature measurement system having plural pyrometry sensors for real-time wafer temperature measurement.
Although the multi-zone illuminator provides improved device fabrication uniformity and repeatability, a number of process control difficulties remain with respect to fabrication by rapid thermal processing (RTP). For instance, in one implementation of rapid thermal processing (xe2x80x9cRTPxe2x80x9d) or rapid thermal chemical-vapor deposition (xe2x80x9cRTCVDxe2x80x9d), a substrate is generally supported by a susceptor during the application of heat. The susceptor can absorb the radiant optical energy and redistribute thermal energy across the substrate thus nullifying or minimizing effectiveness of the control inputs to a multi-zone illuminator. Another limitation relates to the varying emissivity of the substrate during processing due to the dependence of substrate emissivity on temperature and thin films. Although CVC""s multi-zone temperature sensing and control technology in conjunction with multi-zone illuminators can compensate for variations in wafer emissivity (due to any source such as temperature and/or material layers), this compensation can introduce some errors and requires complicated control algorithms which can depend upon extensive testing and calibration runs for each type of substrate being processed. Another difficulty relates to the size and makeup of the susceptor used to support a substrate. The heating susceptor can introduce residue contaminants (e.g., metallic contaminants) to the substrate when the susceptor is in physical contact with the substrate. Also, to provide adequate mechanical support of the substrate, the susceptor can be made of a relatively large mass of thermally conductive material. The larger the mass of a conventional heating susceptor, the more difficult it is to estimate and control the heat energy absorbed and emitted by the susceptor. Moreover, high-thermal-mass susceptors significantly slow down the wafer heating and cooling times, resulting in reduced wafer processing throughout.
Therefore a need has arisen for a method and apparatus that provides improved temperature control and uniformity during thermal processing of a substrate during fabrication of semiconductor devices on the substrate in a thermal processing equipment.
A further need exists for a method and apparatus that provides improved accuracy and repeatability in measuring the temperature distribution of a substrate during thermal processing applications.
A further need exists for a method and apparatus that provides enhanced spatial control of incident optical radiation to improve the accuracy, uniformity, and repeatability with which a multi-zone illuminator heats a substrate in rapid thermal processing (RTP) including rapid thermal chemical-vapor deposition (RTCVD) applications.
In accordance with the present invention, a high-performance radiant energy transfer system and method is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed methods and apparatus for providing energy to a substrate during thermal processing (e.g., in RTP and RTCVD) for the fabrication of a device such as semiconductor chips. A housing-forming a reactor process chamber can be used to isolate a substrate for thermal processing (such as RTA, RTO, RTN, or RTCVD). A radiative heat source such as a multi-zone illuminator can direct radiative energy flux at the substrate to provide thermal energy in support of the thermal fabrication process. An energy transfer device can be disposed between the substrate and the heat source to efficiently and accurately and repeatably transfer energy originated from the radiative energy source to the substrate. The energy transfer device can also substantially decouple the substrate heating as well as temperature measurement and control tasks from the substrate emissivity effects. The energy transfer device can comprise first and second regions, the first regions having a first emissivity and thermal conductivity, and the second regions having a second emissivity and thermal conductivity wherein the first regions can provide a higher degree of energy transfer and the second regions can provide a lower degree of energy transfer. The low energy transfer characteristics of the second regions allow the second regions to act as spacers or energy zone buffers that separate the first regions from each other. In one embodiment, the second regions can be empty spaces formed between adjacent first regions. This arrangement enables excellent multi-zone substrate heating and temperature control via improved controllability of the spatial profile of the incident radiant power on the substrate.
More specifically, the reactor chamber can support any conventional thermal processing system or method for device fabrication onto a substrate, including single-wafer RTP and RTCVD. The radiative energy source can include any known equipment for thermal processing, including the multi-zone illuminator available through CVC, Inc. The radiative energy source can provide thermal energy with conventional tungsten halogen lamps arranged in plural spatially resolved heating zones, such as the concentric or spiral lamp distribution arrangements developed by CVC. The radiant energy provided by the multi-zone illuminator, can be controlled by a multi-zone controller and related temperature sensors associated with each zone and can be adjusted in real time on a zone-by-zone basis by the multi-zone controller associated with the illuminator power supplies and the temperature sensors.
The energy transfer device can include plural energy transfer regions or zones having the first emissivity and/or thermal conductivity, the energy transfer regions disposed so that each first region is associated (in terms of radiant energy transfer) with one or more zones in the multi-zone illuminator. The energy transfer regions can have a high emissivity, meaning that each energy transfer region can absorb (from the illuminator) and emit (mostly to the substrate) all or nearly all of the energy directed at it; and/or, the energy transfer regions can have a relatively high thermal conductivity, meaning that each region can diffuse or distribute thermal energy freely within itself. The energy transfer regions can be separated from each other with plural thermally insulating regions having the second reduced emissivity and/or reduced thermal conductivity.
The thermally insulating regions can have a low emissivity, meaning that they absorb and emit very little or a small fraction of the energy directed at them; and/or the insulating regions can have a low thermal conductivity, meaning that each insulating region resists the diffusion of heat within itself and between neighboring high-emissivity regions. Thus, the thermally insulating regions can divide up the energy transfer regions so that substantially all or most of the radiant energy associated with each zone of the multi-zone illuminator is translated to that zone""s associated energy transfer region (or regions), and so that the energy transfer regions transfer very little thermal energy between each other in the form of heat conduction due to the low thermal conductivity of the thermally insulating regions. In addition, the thermally insulating regions can have special geometric designs to reduce energy absorption, such as a significantly smaller exposed surface area compared to the energy transfer regions (such as small free-space gaps between the high-emissivity regions).
The energy transfer device can comprise a central disk and plural concentric rings disposed about the central disk, the central disk and the concentric rings forming higher-emissivity energy transfer regions. An insulating region can be inserted at the inner circumference of each concentric ring. In one embodiment, the energy transfer regions of concentric rings are comprised of silicon carbide (or aluminum nitride, or graphite, or boron nitride or silicon) and the insulating regions are comprised of free-space gaps. In another embodiment, the energy transfer device can be formed from a single contiguous plate having insulating s regions etched into or embedded in the plate between each alternating energy transfer region (or within the high-emissivity region).
The energy transfer device of the present invention can support thermal processing of various substrates such as silicon through secondary radiation. A radiative energy source having plural radiant energy zones can be directed at the energy transfer device with one or more specific radiant energy zones operable to provide a predetermined and controlled amount of radiative energy (adjustable and controllable in real time). An emissive region can be associated with at least one of each such radiant energy zones to absorb most or substantially all of the radiative energy projected onto the surface of the energy transfer region and to provide secondary radiative energy to the substrate. A temperature sensor can measure the temperature of each emissive region to determine the amount of secondary radiative energy being transferred to the substrate and to extract the projected substrate temperature. A multi-zone controller associated with the radiative energy source can adjust the energy level of each emissive region in real-time by altering the amount of radiative energy provided by the one or more radiant zones associated with each region.
The high performance energy transfer system and method according to the present invention provides important technical advantages. The energy transfer device maps one or more specific zones of a multi-zone controlled radiative energy source to a particular zone on the heated substrate within a processing chamber, thus providing the multi-zone control authority needed for real-time temperature uniformity control and for excellent repeatability of thermal fabrication processes.
Another important technical advantage is that the energy transfer device can be constructed with materials having characteristics which allow accurate and repeatable measurement of each region""s energy level or temperature. Thus, the output signals of the real-time sensors can be used by a multi-zone controller to accurately adjust the energy provided to each region by specific sets of associated zones without any significant interference effects or errors caused by wafer emissivity variations.
Another important technical advantage of the present invention is that the energy transfer device can be placed proximate to but not in contact with the substrate, thus avoiding contamination of the substrate by the energy transfer device. The distance between the substrate and the energy transfer device can advantageously be adjusted to accurately control the secondary radiation pattern projected by the energy transfer device to the substrate (and also the degree of separations of energy profiles from different zones). For instance, the distance between the substrate and the energy transfer device can be arranged so as to be less than the width of the radiation rings (e.g., for a radiation ring width of 5 mm, the distance between the substrate and the energy transfer device is chosen to be preferably in the range of xcx9c1 mm to xcx9c5 mm).
Another important technical advantage is that, in a configuration in which the energy transfer device does not directly support the substrate, the energy transfer device can be constructed of a relatively small mass of a material, resulting in small thermal mass and rapid thermal response. The smaller is the mass of the energy transfer device for a given type of material, the quicker is the response of the energy transfer device to increased energy input, or the removal of energy due to reduced input radiant energy, thus providing faster heating and cooling rates than conventional contact susceptors can provide.
Another important technical advantage is achieved by the partitioning and separation of the energy transfer device into separate zones. These separations preferably have circular symmetry for processing of circular wafers. The average radial dimensions or widths of the segmented pieces are significantly smaller than the radial dimension of a solid plate piece, which allows the use of individually controllable low-thermal-mass parts. Thus, the radial temperature distribution profile of a given radiation transfer ring will be established in a much faster time frame compared with a conventional large-area plate piece of the same thickness. The thickness of the radiation transfer ring, and therefor its thermal mass, can be made much smaller, making this invention suitable for all RTP (e.g., RTA, RTO, RTN, RTCVD, etc.) application.